Having now completed just short of 8K in my 8 month old MKIII I was sitting on a steady long term average of around 56.4 mpg.

 

A bit of careful driving here and there would occasionally notch  it up .1 or and back down again with the opposite.

 

But on Monday this week it has suddenly started fluctuating massively upon acceleration, deceleration , coasting etc.

 

I am definately reading the Long term average, with the other two options been Since start, and Since refuel.

 

I haven't reset anything in the infotainment or even the trip mileage.

 

Any thoughts on what's happening?

It resets itself after a certain period. Not sure if it is time/distance or both. Yours has just reset and will take a while to stabilise.

The "long-term" display resets at 100 hours driving or 10,000 km (~ 6200 miles) driven, whichever happens first.

 

It's on page 48 of my manual.

A sad case of RTFM 

 

Cheers for the heads up. Perhaps my Long term average will actually pick up a bit then, as the car is a bit more run in now.